Electrical coupling system



April F. A. KOLSTER I ELECTRICAL COUPLING SYSTEM Filed March 23, 1926 n I l 7 m Z w M II N W M e50 550 Maw-5R5- E Illlll r FIE E FIE 4 ll'lu'l'lllll.

Freder/c lll Patented Apr. 21, 1931 FEEDE CK rArEu'r center;

1%.. KGLSTER, OF PALO ALTO, CALIFORNIA, ASSIGNOR TO FEDERAL TELE- GRAIPZ-I CCMPAITY, (1F SAN FRANCISCO, CALIFORNIA, A CORPORATION OF GALI- FOR-NIA ELECTRICAL COUPLING SYSTEM Application filed March 2-3, 1926. Serial No. 96,690.

This invention relates to translating circuits for high frequency currents and has as object to provide a circuit having a uniform translating efficiency over a range of frequencies.

It is a common practice to couple radio frequency circuitssuch as the various stages of a vacuum tube amplifier together causing them to act differentially on a sec ondary winding at high frequencies, at which excessive transfer of energy would normally occur, and causing them to act cumulatively on the secondary winding at the lower frequencies, at which insuflicient energy would normally be transferred.

This application is a continuation in part of my co-pending application, Serial llo. 52,497, August 26, 1925.

Referring to the drawings? Figure 1 is a circuit diagram showing the invention as applied to a high frequency amplifier system; V

I Fig. 2 shows the characteristic curves of the reactance values of the coupling impedances.

Fig. 3 shows curves illustrating the effect of increasingthe decrement of the one impedance branch system.

Fig. t shows curves illustrating how the energy transfer ratio may be made substantially constant by this invention.

In Fig. 1 of the drawings this system has been shown as incorporated with a cascade amplifier comprising a plurality of amplifying devices such as electron emission tubes and 11. These tubes are preferably of the three element type and include a grid 12,

electron emission element 13 and plate or anode 1 1. Tube 10 is provided with an input ircuit 15 and an output circuit 16 while tube 11 is provided with a similar input circuit 17 and output circuit 18. The input circuit 15 is coupled to a suitable source of signal energy of radio frequency and accordingly has been shown as provided with a secondary inductance 19 which is coupled to a primary inductance 20, the inductance 20 being connected to an antenna 21 and ground 22. The input ircuits 15 and 17 are connected across the grid and electron emission element of the respective tubes in the usual manner. The electron emission elements 13 are shown as energized by suitable A batteries 23 and 2% while the output circuits 16 and 18 are energized from a suitable source of current such as B batteries 26 and 27, the arrangement of these A and batteries being well known in the art. The output circuit 18 has been shown connected to aftranslator, indicated diagrammatically at 28, such a detector or further anuplifying devices.

As a part of the means for coupling together the output and input circuits 16 and 17 respectively, the output circuit 16 is provided withat least two branch impedance paths 30 and 31 which are preferably reactive. The branch 30 includes an inductance L5 while the branch 31 includes an inductance L and a capacitance C The input circuit 17 is preferably inductively coupled with at least one or it may be coupled with both of the branches 30 and 31 as shown. Good results have been obtained by employing mutual inductive coupling comprising a secondary inductance coil 33 which is connected in series with the input circuit 17 and is positioned in inductive relationsl ip with the inductances L and L the inductance L preferably being spaced farther from the inductance 33 than the inductance L The system is selectively tunable throughout a substantial range of radio frequency by suitable means such as variable condensers 34 and 35 extending across the inductances 17 and 33 respectively.

' The impedance branches 30 and 31 are preferably selected so that their values of reactances correspond approximately to the characteristic curves shown in F ig. 2. In these curves abscissa: represent the frequencies of the selected energy, while ordinates represent reactances which may be either positive or negative according to whether they are above or below the horizontal axis. Thus if it is desired to design the coupling system for the present day broadcast range of from 200 to 550 meters corresponding to the vertical lines 32 and 36. the inductance L is sc lected so that its reactance may be represented by the curve 2 which will be straight inclined line above the horizontal axis as inductive reactance varies in direct proportion to frequency. The impedance branch 31 has the respective values of its inductive reactance L and capacitative rcactance C proportioned so that the reactance of this branch will remain negative throughout the desired freqlqency range as represented by the curve 1. he values of the various rcactanccs are also made such that the total reactance of the two branches 30 and 31 in series may be represented by the dash-dot curve 3 while the total reactance of the two branches in parallel, or that of the output circuit 16 may be represented by the dash-double-dot curve 4. The resonance frequency of the output circuit or the frequency at which the rcactance of the two branches in parallel approaches infinity is represented by a vertical line 37 and is located just below the lower frequency limit of the frequency range. Thus, the resonance point has been shown as located at a frequency corresponding to 650 meters. The two branches 30 and 31 taken in series will be resonant at a point where their combined re actance is zero or the point at which the curve 3 intersects the zero reactanee line. This point will also fall approximately upon the 650 meter line 37.

With the arrangement as described above, electrical energy of a given radio frequency in the output circuit 16 will divide between the two branch impedance paths 30 and 31 in accordance with the reactance values sumed by these branches. Since the reach ance of the branch 31 is negative and that of the branch 30 positive, a circulatory current will be set up between the two branches, the magnitude of this circulatory current depending upon the relative reactances of the branches and therefore dependent upon the selected frequency. For the higher frequencies near the 200 meter limit the reactance of the branch 31 will have small negative values so that the circulatory current will be negligible and transfer of energy between the circuits 16 and 17 will occur through the differential effect of the inductances L and L upon the secondary inductance It will be noted that the current in the output circuit IS-Will produce opposed magnetic fields in the coils L and L as the branch currents will flow in opposite directions. Therefore, for at least a portion of the frequency range currents can be induced in the input circuit 17 by the differential effects of the currents in inductances L and L However, as the system is tuned for longer wave lengths or lower frequencies the transfer of energy will occur chiefly as the result of magnetic effects produced by the circulatory current which acts cumulatii'cly upon the coils L and L to induce current in the secondary inductance 33.

Thus by properly selecting the reactance values the resultant magnetic field tending to induce current in the secondary coil 33 can be made to remain substantially constant and independent of frequency variations so that a constant proportion of the energy in the circuit 16 is always transferred to the circuit 17. Not only is this system useful from the standpoint of obtaining constant efficiency but it is also advantageous in case it is desired to operate the amplifier 10 regeneratively. Thus if a certain amount of energy is fed back to the input circuit 15 so that this tube operates rcgeneratively, then the react-ance values of the impedance branches maybe adjusted so that this regenerative condition is maintained throughout the frequency range without further adjustment.

The above arrangement gives approximately the results desired but the energy transfer ratio may be held to a closer constant by increasing the decrement of the output circuit 16. This is preferably accomplished by inserting a substantial resistance 40 in serles with the impedance branch 30, such as a resistor of about 10 ohms. Fig. 3 shows the effect of this resistance upon the resonance of the output circuit. The dotted curve 5 illustrates how the resonance without the resistance 40 is relatively sharp or in other words the resistance rises suddenly to a maxi mum at the point of resonance. This peak is of course located beyond one limit of the dcsircd frequency range, but it causes the percentage or energy transferred to be less for frequencies intermediate the limts of the frequency range than for frequencies near the limit thereof, as illustrated by the dotted curve 6 in Fig. 4. The effect of the resistance 40 is indicated by the curve 7 which shows that the decrement of the output circuit is increased, or in other words the resonance peak is made less abrupt. The effect of increasing the decrement of the output circuit is indicated by the curve 8 in Fig. 4 which is substantially a straight horizontal line showing that the intermediate frequencies are now transferred at substantially the same efficiency as the frequencies near the limits of the range. Another important function is served b the resistance 40 in that by adjusting t e value of this resistance between llfl certain limits the circulatory currents in the branches 30 and 31 may be controlled for any one frequency without changing the natural period of the output circuit. This adjustment is very advantageous as it is proposed to employ a plurality of these coupling devices with a cascade amplifier and to 0perate the condensers 35 by means of a gang control. In such a system an individual coupling device may be adjusted by making variations in the resistance 40 without making a corresponding adjustment for an individual condenser 85. The capacitance C is also preferably made adjustable or variable between certain limits so as to provide some means for effecting a variation in the relative reactances of the branches 30 and 31.

It is to be understood that the invention is not to be limited to impedance values which will produce the various curves illustrated in the drawing. Various modifications of these values may be made without departing from the spirit of the invention as defined in the appendedclaims. The curves shown in Fig. 4.- are approximations for the purpose of illustrating the effect of the resistance 40.

I claim:

1. In a radio frequency amplifying system comprising amplifying means having input and output circuits, means for coupling another circuit to said output circuit in a differential relation, said coupling means comprising inductances responsive to the amplified energy for controlling the proportional amount of energy transferred at different frequencies, means for selectively tuning said coupling means, means connected in series with said selective tuning means for controlling the ratio of energy transfer for a given frequency without affecting the tuning of the coupling means and connections from said output circuit to points intermediate said inductances and between said tuning means and said controlling means.

2. In a system of the class described comprising two electrical circuits, the first adapted to transfer oscillatory electrical energy to the second, at least two impedance branches in said first circuit, each branch including an inductane, a variable resistance in series with one inductance, a variable capacity in series with the other inductance, means for inductively coupling said second circuit to both said inductances in a differential relation and connections for impressing variable potential at points intermediate said inductances and between said variable resistance and capacity.

3. In a system of the class described comprising two electrical circuits, the first adapted to transfer oscillatory electrical energy to the second, at least two impedance branches in said first circuit, each branch including an inductance coil, a resistance in series with one coil and a condenser in series with another coil, means for inductively coupling said second circuit to both said inductances, the fields induced by the current in said one circuit being opposed and means for impressing a high potential intermediate said coils and between said resistance and condenser.

4. In a system of the class described comprising two electrical circuits, the second being adapted to receive oscillating energy from the first, at least two inductances electrically connected with the first circuit, a third inductance in the second circuit inductively coupled to the first two inductances, means for selectively tuning said system throughout a substantial frequency range, and a resistance in series with said first two inductances for controlling the transfer of energy to said second circuit by their differential effect for at least a portion of said frequency range.

5. In a system of the class described comprising two electrical circuits, the second adapted to receive radio frequency energy over a substantial frequency range fromthe first circuit, a pair of reactive means included in the first circuit, one of said reactive means having a resonance period just beyond one of the limits of said frequency range, means for selectively damping said first circuit and means for coupling said second circuit to one of said pair of said reactive means.

6. In a system of the class. described com-,

prising two electrical circuits, the second adapted to receive radio energy over a substantial frequency range from the first circuit, reactive means included in the first cir- I cuit having a resonance period justbeyond one of the limits of said frequency range, means for coupling said second circuitto said reactive means, and means connected in series with vsaid reactive means for varying. the

characteristic energy transfer curve for said range.

7. In a system of the class described comprising two electrical circuits, the second adapted to receive radio frequency energ from the first, at least two reactive impedance branches included in said first circuit, one of said branches including a resistance and an inductance, and the other of said branches ineluding an inductance and a condenser, means for applying a potential to said first circuit across an intermediate point in said inductance and intermediate said resistance and said condenser and means for coupling said second circuit to at least one of said branches.

8. In a system of the class described comprising two electrical circuits, the second being adapted to receive energy from the first over a given frequency range, and means for electrically coupling said circuits together comprising at least two parallel reactive impedance branches in said first circuit, said THU branches in parallel having a resonance period at a frequency located outside said freuency range, and means for increasing the decrement of said branches.

9. In a system of the class described comprising two electrical circuits,the second being adapted to receive oscillatory energy from the first over a given frequency range, and means for electrically coupling said circuits together comprising at least two parallel reactive impedance branches included in the first circuit, the relative values of said impedances being such that the resonance period for said first circuit lies outside but adjacent one limit of said range, and means for damping said first circuit.

10. A coupling system for effecting transfer of oscillatory energy between two circuits comprising two parallel reactive impedance branches included in one circuit, one of said branches including an inductance and a substantial variable resistance, and the other branch including an induc ance and a capacitance, connections for impressing an exciting potential across an intermediate pointin said inductance and between said variable resistance and capacitance and means for inductively coupling the other circuit to at least one of said branches.

11. A coupling system for effecting transfer of oscillatory energy between two circuits comprising two parallel reactive impedance branches included in one circuit, one of said branches including an inductance and a substantial variable resistance, and the other branch including an inductance and a capacitance, connections for introducing an exciting potential across an intermediate point of said inductances and a point between said variableresistance and capacitance and means for mutually inductively coupling the other circuit to at least one of said branches.

12. In a system of the class described comprising, energy amplifying means having control and output circuits, two branch reactive impedances in said output circuit, another circuit coupled to at least one of said branches, means for selectively tuning the system through a given frequency range, one of said impedances having a negative value of reactance for the lower limit of said frequenc range, the natural period of both branc es in series being below the lower frequency limit of said range and the natural period of said output circuit being above said frequency range, and means for substantially increasing the decrement of said output circuit.

13. In a radio frequency amplification circuit comprising a plurality of electron tubes 9. coupling system interlinking the output circuit of one tube with the input circuit of a succeeding tube, said coupling system including an inductance, a pair of branch cir units, one of said branch circuits including a variable resistance and one ortion of said inductance, the other of said ranch circuits including a capacity and another portion of said inductance, the portions of said inductance and said branch circuit being differentially connected in said output circuit, an inductance disposed in the input circuit of said succeeding tube and coupled with said aforementioned inductance, said branch circuits being conjointly tuned to resonance at a wave length longer than the longest wave length to be received, and said branch circuit including inductance and capacity in series being tuned to resonance at a wave length shorter than the shortest wave length to be received for effecting a uniform transfer of energy over a predetermined wave length ran ge.

14. In a system of the class described comprising two electrical circuits, the second being adapted to receive oscillatory radio energy from the first over a substantial frequency range, and means for electrically coupling said circuits comprising at least two parallel reactive impedance branches associated with the first circuit, one branch including an inductance and a substantial resistance, and the other branch including an inductance and a series capacitance, said inductances and capacitance being so proportioned that said two branches have two different points of resonance so that different degrees of coupling are provided for different frequencies within said range, said resistance serving to dampen the first circuit.

In testimony whereof, I have hereunto set my hand.

FREDERICK A. KOLSTER. 

